Effects of insulin and diet on the metabolism of l(+)-lactate and glucose by the perfused rat heart

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Abstract
The removal of L(+)-lactate and glucose, the formation of lactate, the consumption of oxygen and the changes in glycogen content were measured in the perfused rat-heart preparation described by Bleehen and Fisher (1954). L(+)-Lactate, glucose and insulin, alone and in combinations, were added to the perfusate, and hearts from well-fed and 24-hr.-starved rats were studied. Lactate when added as sole substrate (5 m[image]) contributed 52% to the respiration of hearts from fed rats, and glucose (5 m[image]) contributed 24%. Insulin was without effect on lactate oxidation but increased the contribution of glucose to 57%. Lactate decreased the oxidation of glucose in the presence or in the absence of insulin, and stimulated glycogen synthesis from glucose. Glucose in the absence of insulin decreased lactate oxidation by 25%, but in the presence of insulin lactate oxidation was completely suppressed. Starvation increased the rate of glycogenolysis, but decreased the total oxidation of lactate, glucose and glycogen, whether glucose, lactate and insulin were added singly or in combinations to the perfusate. The maximum anaerobic rate of glucose uptake was about five times the maximum insulin-induced rate of glucose uptake aerobically.